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Huntsman Lake Dam Rehabilitation Project Huntsman Lake Dredging and Restoration Department of Public Works and Environmental Servcies
Citation preview
Huntsman Lake Dam RehabilitationHuntsman Lake Dredging and Restoration
Department of Public Works and Environmental Services Fairfax County, VA
A Fairfax County, VA publication September 2012
• Dam Rehabilitation – Background– Major design elements– Easements– Mitigation for tree and wetland loss
• Lake Dredging and Restoration– Sedimentation – Dredging options and approach– Lake restoration
• Timeline for Projects and Coordination
Huntsman Lake Dam RehabilitationHuntsman Lake Dredging and Restoration
Outline
Huntsman Lake Dam Rehabilitation Project Background
• Huntsman Lake Dam is a 41.5 feet high earth‐fill dam built in 1973 as flood‐control dam by the Natural Resources Conservation Service (NRCS). Fairfax County and the Northern Virginia Soil and Water Conservation District (NVSWCD) were the local sponsors.
• It was the second of six dams built by the NRCS in the Pohick Creek watershed
Huntsman Lake Dam Rehabilitation Project Background
• The dam drains an area of 1,482 acres (2.3 square miles)• Land‐use in the drainage area is 73 percent residential and 22 percent
woodland or open space
Huntsman Lake Dam Rehabilitation Project Background
• The dam impounds a 28.6 acre lake at normal pool, with a floodwater retarding pool area of 60 acres
• Huntsman Lake Dam is regulated by the Virginia Department of Conservation and Recreation (DCR), Division of Dam Safety
Huntsman Lake Dam Rehabilitation Project Background
• Huntsman Dam operates under a conditional Operation & Maintenance (O&M) Certificate from DCR because its auxiliary spillway can only convey about 50 percent of the flows from the design storm.
Huntsman Lake Dam Rehabilitation Project Background
• In 2010, NRCS in collaboration with Fairfax County and NVSWCD initiated a rehabilitation project for the Huntsman Lake dam
• Fairfax County contracted with Schnabel Engineering to provide engineering and ancillary services for the project
• A local task force was formed to provide input on community concerns, and a number of task force meetings and public meetings were held in 2010 and 2011
• A rehabilitation plan was developed by NRCS collaboratively with Fairfax County and NVSWCD and released in September 2011
• Design work by Schnabel Engineering was initiated shortly after the release of the rehabilitation plan, and a final design submitted in August, 2012
Huntsman Lake Dam Rehabilitation Project Summary of rehabilitation plan
Huntsman Lake Dam Rehabilitation Project Major Design Elements
Huntsman Lake Dam Rehabilitation Project riser replacement
Huntsman Lake Dam Rehabilitation Project riser replacement
Huntsman Lake Dam Rehabilitation Project spillway realignment and armoring
Huntsman Lake Dam Rehabilitation Project spillway realignment and armoring
Huntsman Lake Dam Rehabilitation Project spillway realignment and armoring
Huntsman Lake Dam Rehabilitation Project Easements
A public hearing for the required easement on Lakewood Hills Community Association #1 property is planned for December 4, 2012
Huntsman Lake Dam Rehabilitation Project mitigation for tree and wetland loss
Huntsman Lake Dam Rehabilitation Project Summary
• In 2010, NRCS in collaboration with Fairfax County and NVSWCD initiated a rehabilitation project for the Huntsman Lake dam
• Final design for the project has been completed by Schnabel Engineering and is awaiting approval by NRCS and Fairfax County
• Permit applications have been prepared for the project and will be submitted shortly
• A public hearing for an easement required on Lakewood Hills #1 Homeowners Association property is proposed for December 4th, 2012
• Mitigation for tree and wetland loss as a result of the project is proposed on the lake shoreline and on Middle Run upstream of Huntsman Boulevard
Huntsman Lake Dredging and Lake Restoration Background
Huntsman Lake Facts• Drainage Area = 1,482 acres (2.3 square miles)• Lake Surface Area = 28.6 acres• Sediment Pool Capacity = 295,000 cubic yards (CY)• Current sediment in lake = 65,000 CY• Estimated annual sediment load = 2,970 CY
32.5 feet
65,000 CY
Sediment Thickness
Water Depth
2011
Inactive Dewatering Basin
Lake Restoration and Dredging Project
Project Goals• Restore sediment pool capacity
– Downstream water quality benefits– Lake water quality– Esthetics
• Improve lake water quality and habitat• Provide long term maintenance improvements
Dredging Alternatives
1. Mechanically dredge and
haul wet
2. Drain lake and dry in place
before hauling
3. Hydraulically dredge and
dewater on shore in Geo-
textile bags
PRE‐DREDGING: An estimated 35,000 cubic yards of sediment accumulated in the lake forming islands and reducing water levels to less than three feet in most areas.
Lake Barton Example
Lake Barton: Pre-Dredging
Lake Barton: Dredging in Progress
Lake Barton: Dredging in progress
Lake Barton: Dredging in progress
Lake Barton: Completed Project
Option to Drain LakeLake Needwood in Montgomery County, MD
Option to Drain Lake
33
Option to Drain LakeLake Needwood in Montgomery County, MD
Huntsman LakePhase 1 Dredging 30,000 Cubic Yards
Huntsman LakePhase 2 Dredging up to an additional 35,000 Cubic Yards
Lake Restoration
• In‐lake forebay• Wetland planting• Shoreline stabilization• Fish habitat• Fish stocking
Lake Barton: Fish stocking by Virginia Game and Inland FisheriesFish habitat created from salvaged trees
Shoreline Restoration
Shoreline RestorationHuntsman Lake Existing Conditions
Shoreline Protection Options
Fish Habitat Structures
Huntsman LakeSite Access and Staging Area
2011
Huntsman Lake
Huntsman Lake Dam RehabilitationHuntsman Lake Dredging and Restoration
Project timeline and coordination • Project agreement between Fairfax County, NVSWCD and NRCS
(for dam rehabilitation) expected to be executed by February/March, 2013
• Project bidding and contract award: approximately 2‐3 months• Project duration: 8‐9 months• Lake will remain drained for entire project• Drawdown will be controlled to allow fish to migrate downstream
to the greatest extent possible• Dam rehabilitation and dredging projects will be coordinated to
minimize the time lake is drained• Lake filling after project completion is dependent on rainfall
conditions
Huntsman Lake Dam RehabilitationHuntsman Lake Dredging and Restoration
For more information or to request this information in an alternate format, call the Stormwater Planning Division, Department of Public Works and Environmental Services, Fairfax County 703‐324‐5500
TTY 711 or email SWPDmail@fairfaxcounty.gov
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